This invention relates to a water cooling system for an engine, employable in connection with a marine propulsion unit; and more specifically, to a valve arrangement for controlling coolant flow through the cooling system.
It has been known to employ an engine as a powering means in connection with marine propulsion units. Cooling systems in such engines have included means for introducing a coolant, such as water from the body of water within which the marine craft is operated, into the engine. Valving arrangements have commonly been employed to control the flow of coolant through the engine, in order to maintain desired engine temperatures during operation.
Concerning such valve control arrangements, it has specifically been known to include both a thermostatically controlled valve and a pressure actuated valve for controlling coolant flow. Such a system employing both a thermo-sensitive control valve and a pressure-sensitive control valve has been disclosed in Japanese Unexamined Patent Publication Sho61-48687. The thermo-sensitive valve primarily controls the coolant flow under low RPM operating conditions. The maximum amount of coolant which will flow through the engine as a result of the opening of the thermo-sensitive control valve, however, may not be sufficient to allow proper cooling of the engine under higher loads. To increase the flow of coolant in the high RPM range, where the thermal load of the engine is higher, a pressure-sensitive control valve is provided.
However, certain problems have been encountered when utilizing known pressure-sensitive valves for the above-discussed purpose. For example, sufficient water flow cannot be achieved in the high RPM operation range when a pressure-sensitive control valve 1 of the type shown in FIG. 1 is used. Although the valve body 2 will become unseated, thereby opening the valve device 1, when the pressure rises on the water jacket side (indicated by the arrow accompanying the notation "in"), the valve body 2 will immediately return to its seated, closed position, under the force of the spring member 3, due to a resulting subsequent drop in pressure on the water jacket side. Accordingly, repeated opening and closing of the valve device will occur, thereby rendering adequate water flow impossible to achieve.
The valve device 4 of FIG. 2 overcomes some of the problems of the device of FIG. 1 by retarding such closing of the valve body 5 immediately after opening via a diaphragm 6 exposed to atmospheric pressure. However, the valve device 4 requires the use of a throttling area 7 along the discharge passage 8 in order to achieve such results. The throttling area 7 impairs the achievement of a sufficient water flow.
It is, therefore, a primary purpose of this invention to provide an improved water flow control arrangement for use in a water cooling system for the engine of a marine propulsion unit.
It is yet a further object of this invention to provide an improved pressure-sensitive valve device for such a water cooling system which allows the achievement of a sufficient coolant flow rate in the high RPM operation range of an engine.